Structure and Function

Dr. Lanning is a cellular and molecular biologist and a member of Hope Protestant Reformed Church, Redlands, California.

From whom the whole body fitly joined together and compacted by that which every joint supplieth, according to the effectual working in the measure of every part, maketh increase of the body unto the edifying of itself in love. Ephesians 4:16

Scripture is the ultimate guide for believers to many marvelous aspects of creation, allowing them to contemplate God’s wisdom, power, creativeness, and majesty. God is to be thanked for teaching us how to give Him praise through thoughtful mediation on His creation. Today, our ability to observe the Creator’s handiwork has been providentially expanded many fold compared to preceding generations. Our ability to observe the heavens reaches so much farther than David’s in Psalm 19. Likewise, our knowledge of the wide variety of the creatures of the deep is broader than the author of Psalm 104 could know. Because we have been given this insight, we are obligated to take a moment to contemplate how they reflect the Creator’s praiseworthiness. So let us do that with just a few examples. In our expanded capacity to do so, we would be foolish not to.

An argument can be made that advances in man’s understanding of microscopic and sub-microscopic particles in cells dwarf the advances of any other scientific field. In particular, the discovery of the mechanisms by which biological molecules work to support life has risen exponentially over the past two or three generations. We have been given the ability to know and contemplate entire categories of biology never before accessible to us. Out of these new categories of knowledge a principle has emerged that is foundational for all aspects of biology: the structure-function relationship. While it has long been appreciated that an organism’s unique structural characteristics are well suited for its various functions (the wings and webbed feet of ducks provide them capable mobility in both air and water), structure-function relationships at the molecular level are so intricate that minute changes in the structure of a single molecule can cause a duck to have no wings or non-webbed feet. Scripture also speaks of a structure-function relationship in the verse quoted at the heading of this article. In Ephesians 4:16, Paul informs us that human bodies and the body of Christ are both constructed or structured to make possible their designated ends: the human body’s wide range of motion is possible because of its structure, while the body of Christ is structured to edify itself in love so that it reaches healthy maturity.

So fundamental is the concept of structure-function relationships to biology that it is woven into the very fabric of every cell biology and biochemistry course, from the introductory to the graduate levels. Students who are paying attention will soon realize that if they spend time learning how to understand molecular structures, then understanding and even predicting molecular functions will easily follow. In this context, structure simply means shape or architecture. Every molecule has a specific shape that is a direct result of the number and type of atoms from which it is made. For example, water molecules have a specific shape due to the arrangement of the one oxygen and two hydrogen atoms that form the molecule (water happens to have a boomerang like shape). Along with a specific shape, additional physical characteristics are included in the concept of structure. Following our example, the oxygen atom in a water molecule has a partial negative charge while the two hydrogens have partial positive charges. Therefore, contained within the structure of a water molecule is a boomerang like shape with both partial positive and negative charges. Water has myriad functions in biology, from serving as the most common solvent to providing the raw material for photosynthesis, and each function is a direct result of the structure that we just reviewed.1 Hopefully, this example clearly demonstrates the concept of structure function relationships: the physical shape and associated characteristics of each molecule and component in a cell are directly responsible for and govern the functions of that molecule or component.

Structure-function relationships at the molecular and cellular level are so sophisticated and critical for life that it is impossible not to stop and wonder as one learns about and studies them. It is my experience that when students themselves begin to recognize molecular structure function relationships, their excitement for biology is the greatest. When delving into some of the more complex structure-function relationships, students will quite literally be left speechless as they contemplate how the remarkably complicated molecules that they are studying work in concert with other molecules to carry out a biological function. And further, that these molecules have to be just so in order for them to function properly, and therefore, for cellular life to exist. Enthusiastic discussions often follow these quiet moments of wonder as students begin to appreciate more fully the relationships.

Today, the Creator has providentially allowed us to know and understand many of the most precise and critical structure-function relationships that He uses to maintain life. As we contemplate a few of these, links to images or videos will be provided in the footnotes. An effective way to meditate on something for the purpose of praising the Creator is actually to behold and carefully observe it (Job 37:14-18). Interested readers are encouraged to do this through the provided links.2

Cell Replication

Cell replication is necessary for living organisms to grow (from fertilization to a fully-grown adult, humans transition from a single cell to trillions of cells), to heal wounds, and to maintain healthy tissues. In order for cells to replicate, they must first duplicate all of their genetic material and then equally divide that genetic material into two new cells. Genetic material comes in the form of the molecule, DNA, and in humans each cell that will divide contains 46 large DNA molecules called chromosomes. A long and complex series of structure function relationships is utilized to duplicate each of these 46 chromosomes, and then to attach each chromosome to its duplicated partner. Next, long tendril-like molecules called microtubules capture and corral the joined, duplicated chromosomes into the very center of the cell, lining them up with one set of 46 chromosomes facing one end of the cell and the other set facing the other end. Finally, the microtubules pull each set of 46 chromosomes to opposite ends of the cell, and the cell splits down the middle, forming two new cells, each with exactly the correct number of chromosomes. Throughout all of this, biological molecules called proteins are engaging in extremely specific interactions based on their unique structures to coordinate each step of the process. If a cell does not perfectly select one set of 46 chromosomes for each cell, the replicated cells will either self-destruct or not function properly. Life would not exist without proper cell replication, and this entire complex process is governed by dozens of structure-function relationships.3

Cell Transportation

Cells are constantly transporting items from one region to another, and while simple diffusion and random motion are responsible for a portion of this transport, the Creator has developed a much more regulated method for the transport of many cellular items. This method of transport utilizes molecular complexes called motor proteins and molecular tracks. Dozens of rigid tracks extend through the three-dimensional space of each cell, and it is on these tracks that motor proteins carry their cargo. Motor proteins typically consist of two, long stalk-like structures twisted around each other, each with bulging ends. One end is perfectly suited to bind a particular cargo and the other end is perfectly suited to bind the tracks extending through the cell. Additionally, the end of the motor protein attached to the track can bind and a molecule that is the cellular form of energy. By harnessing this molecular energy, this end of the motor protein can literally take steps along the cellular tracks, dragging its cargo along with it. The odd structure of these motor proteins in conjunction with the structures of the cellular tracks and energy molecules combine to carry out the critically important function of cellular transport.4

Protein Synthesis

One of the most fascinating structure-function relationships is that of the ribosome. It is commonly known that hereditary information is stored in the molecule, DNA5, and that this information storage is hugely important for essentially all aspects of biology. However, storing hereditary information alone is not helpful for biology. This information must be “read,” processed, and utilized for biological processes to occur. The hereditary information in DNA is used to construct proteins, and it is proteins that are responsible for virtually all biological actions. This is why hereditary information in DNA is so important: DNA stores the information for constructing proteins. The ribosome is the ultimate molecular complex that is able to decipher hereditary information and produce proteins. Prior to the action of the ribosome, another cellular process transcribes the hereditary information in DNA molecules into a related molecule called mRNA. mRNA, which resembles a molecular string, then carries the hereditary information to the ribosome. When an mRNA molecule comes into contact with a ribosome, the ribosome begins scanning the structure of the mRNA molecule for the information that it contains.

It is here that the structure-function relationship is perhaps most strikingly demonstrated. Hereditary information is actually encoded in the very structure of mRNA molecules, and the structure of the mRNA molecule was constructed directly based on the shape of the preceding DNA molecule. Therefore, the Creator has designed ribosomes so that they deftly assess the structure of an mRNA molecule (information), and from surveying that structure, they construct a protein molecule. 6 This is the process that gives each living creature its unique set of heritable characteristics. Subtle changes to the structure of hereditary molecules (DNA and mRNA) can result in ribosomes constructing a protein with a subtly different shape. Small changes in protein shapes can have large effects on the protein’s function. In fact, multiple devastating genetic diseases arise due to miniscule changes in DNA structure.

Cellular Respiration

When performing their various functions, cells use a lot of energy. This cellular energy is harvested from various molecules, with carbohydrates being the most commonly used. Energy present in carbohydrates (and any other energy-carrying molecule) exists precisely because of the particular structure of that molecule. Therefore, the structure of a molecule is energy. However, cells cannot just grab a carbohydrate and use its energy. The energy stored in carbohydrates is in a configuration (structure) that is not directly available to cells. Cells must first transform the energy in carbohydrates into a usable form (structure). The processes of cellular respiration take the molecular energy in carbohydrates (and other molecules) and transform it into a different energy storage molecule called ATP. While structure-function relationships govern all aspects of cellular respiration, two structures at the end of these processes stand out.

The first is a compartment or space within a larger structure called the mitochondrion. Mitochondria (plural) are large complexes where much of our metabolism takes place. Mitochondria are three-dimensional objects with two layers, analogous to one elongated balloon inside another elongated balloon, with a small space between these two layers. When carbohydrates are metabolized, large amounts of hydrogen ions accumulate in the space between these two layers. The accumulation of hydrogen ions in this space is similar to the accumulation of water behind a hydroelectric dam. Just as the water behind the dam can be forced to flow through hydroelectric generators to create electricity, so the hydrogen ions are forced through the second notable structure: a molecular motor. This molecular motor in mitochondria actually looks like a motor, as it has a large central rotor and a drive shaft in combination with other “machine” parts. As hydrogen ions flow through the center of this motor, the rotor and drive shaft spin, and in doing so produce the molecule ATP, which contains energy in a form that cells can use.7

The molecular and cellular structure-function relationship is not a human invention. These intricate relationships were conceived and brought forth by the Most High, who excels in wisdom and knowledge far surpassing any human imagination. Contemplate the orchestration of cell replication. Marvel at the mechanism of cell transportation. Stand in awe at the actions of the ribosome. Issue forth praise for the creativity exhibited in the components of cellular respiration. In all of these creatures, the wisdom, power, and glory of the Creator are on display. Let us give Him due praise for this.

1 For a more thorough and edifying presentation of the structure and functions of water, see Mr. Joel Minderhoud’s article in the May 1, 2014 issue of the Standard Bearer.

2 A model video demonstrating the breathtaking variety of structures and functions in cells can be viewed here: This video is notable in that most of the structures depicted are remarkably accurate representations of the molecules that they depict.

3 This process in real cells can be viewed here: The red components are chromosomes and the green components are microtubules. Notice how the cell “struggles” to get the last chromosome to line up correctly.

4 A model video of motor proteins can be viewed here:

5 DNA was definitively proved to be the molecule of heredity in 1953.

6 A model video of this process can be viewed here:

7 A model video of the amazing structures in mitochondria can be viewed here: The motor process can be viewed here: Please excuse the gratuitous reference to intelligent design at the end of the video.